During neurological or other procedures to the head and neck areas of a patient, it is common for the patient to lie on a table with the patient's head at or extending beyond the end of the table. A head support, designed to hold the patient's head during a surgical procedure, is mounted on a swivel adapter that, in turn, is mounted on a mechanical connector or “base unit.” The base unit is attached at the end of the table. The base unit has movable elements that permit the head support and swivel adapter to be adjusted and clamped at a position and orientation having a desired elevation and longitudinal position with respect to the table. The head support may be a skull clamp which securely and rigidly holds a patient's head in the desired position and orientation. Alternatively, the patient's head may be supported by a head rest, for example, a horseshoe-shaped headrest, or general purpose headrest.
Typically, the head support is coupled to one end of the swivel adapter which is an angled connector preferably providing two degrees of rotational freedom. The other end of the swivel adapter is connected to an upper end of a swivel arm or transitional arm of the base unit. The transitional arm is used to change the elevation of the head support. A shaft on the other end of the transitional arm is located within a bore of one end of the base unit handle. The other end of the base unit handle is rotationally coupled to a generally U-shaped frame which may be longitudinally and/or laterally adjusted with respect to the end of the table. Therefore, by rotationally adjusting the transitional arm with respect to the frame, and further adjusting the position of the frame relative to the table, the head support can be moved into any desired position and orientation.
The transitional arm and base unit handle are locked in desired positions and orientations by operating a closing handle on the base unit handle. One end of a cam rod in the base unit handle is pulled to apply locking forces at both ends of the base unit handle. The locking forces slightly collapse relieved openings that intersect holes at opposite ends of the base unit handle, thereby locking the base unit handle to the shaft on one end of the transitional arm and the U-shaped frame.
While such a construction has proven satisfactory, recent surgical procedures require that more devices be mounted in the area of the head support and swivel adapter, for example, reference arms of a navigation system. To facilitate such devices, it is known to connect an auxiliary arm to a starburst connector on an outer side of the skull clamp. The auxiliary arm has starburst connectors at opposite ends of the arm to which additional devices may be attached. With the auxiliary arm mounted on the outer side of the skull clamp facing outward from the swivel adapter, it is then necessary that the swivel adapter be mounted to a starburst connector on an inner side of the skull clamp facing inward toward a patient and the operating table. Such an arrangement requires that a user reach around the skull clamp and the patient's head in order to adjust and manipulate the swivel adapter. Such an arrangement is awkward in use; and therefore, there is a need to provide a capability of mounting additional devices while maintaining the swivel adapter on the side of the skull clamp facing outward from the swivel adapter and generally toward the user. With such an arrangement, all of the devices can be easily and quickly manipulated by the user.
When additional devices are mounted in the area of the head support and swivel adapter, an additional load is imposed on the base unit handle. Thus, the clamping forces applied by the base unit handle must be correspondingly greater in order to hold the skull clamp and swivel adapter stable during the surgical procedure. With known base unit handles, the closing handle directly creates the locking forces; and a substantial force must be manually applied to the closing handle in order to provide the necessarily greater clamping forces to support the additional devices. While some persons may have the physical strength to apply such larger forces to the closing handle, others may not; and consequently, the base unit handle may slip or move slightly during use. Therefore, there is a need to provide a base unit handle that can be operated to provide the clamping forces necessary to support additional devices on the swivel adapter without requiring a proportionally greater force to operate the closing handle.